Light detection and ranging (lidar) bathymetry is a technique capable of measuring the depth of a relatively shallow body of water (e.g., less than 2 meters). A pulsed laser beam is transmitted from the lidar instrument to the body of water. The light generated by the laser beam is typically in the blue-green portion of the spectrum due to the high transmission through water of light at that wavelength. Portions of the laser pulse scatter from the air/water interface, the water volume, and the floor of the water body back to and are collected by the instrument. The times of flight of the detected signals are converted into range measurements and, upon consideration of viewing geometry, propagation paths, and associated errors, permit determination of the probed water depth.
Depth measurement in the shallow water regime is challenging due to system bandwidth limitations of traditional bathymetric lidar techniques. Traditionally the approach used to resolve two scattering objects separated in range is by resolving the difference in travel time of light between the two objects. The limiting factor in resolving the range between targets in traditional systems is dictated by the pulse width of either the laser pulse or the detection electronics, often defined as cτ/2n, where c is the speed of light, n is the index of refraction of the media, and τ is the limiting pulse width in time (or the inverse of the system bandwidth). Consequently in shallow depth applications the limit of current lidar technologies occurs where ambiguities exist between surface scatterings, volume scattering along the water column, and floor scattering due to system bandwidth limitations associated with laser and/or detector pulse widths. As a result, present day bathymetry lidar systems are limited to depth measurements no shallower than tens of centimeters.
There is a need in the art to improve the precision and other aspects of bathymetry lidar systems.